Field of the Invention
This invention relates to a guidance method for a system for locating wells in a sea floor which are to be drilled from a floating vessel.
In recent years there has been considerable attention attracted to the drilling and production of wells located in water. Wells may be drilled in the ocean floor from either fixed platforms in relatively shallow water or from floating structures and vessels in deep water. The most common means of anchoring fixed platforms includes the driving, or otherwise anchoring, of long piles in the ocean floor. Such piles normally extend above the surface of the water and support a platform attached to the top of the piles. This works fairly well in shallow water but, as the water gets deeper, the problems of design and accompanying cost become prohibitive. In deeper water, it is common practice to drill from a floating structure.
In recent years there has been considerable attention directed toward many different kinds of floating structures. One system receiving attention is the so-called Verically Moored Platform. Such a platform is described in U.S. Pat. No. 3,648,638 issued Mar. 14, 1972, Kenneth A. Blenkarn, inventor. Key features of the disclosure in that patent are that the floating platform is connected to an anchor only by elongated parallel members and the floating structure has buoyancy means designed especially with respect to the trough of a design wave so as to minimize variations in vertical forces imposed on the vertically elongated members which may be caused by passing waves. The are other types of floating drilling structures such as the semisubmersible and the floating drilling vessel with a "moon pool" or vertical opening through the center through which drilling operations are carried out. The drilling engineer selects a floating vessel which he believes will best fit the environmental conditions which are expected to be encountered.
The closest prior art relating to my invention, to the best of my knowledge, concerns frames on the ocean floor having a vertical passage through which a well may be drilled. The drilling tool is guided into the vertical passage by cables extending from the frame to a floating vessel. None of the prior art has means for sequentially guiding drilling pipe or mechanisms successively through each of an array of vertical holes through a sea floor template.